Protein aggregation and amyloid deposition characterize a variety of neurodegenerative disorders including Alzheimer's Disease and Huntingtin's disease. The conversion of a native protein into mature amyloid fibril is a complex, poorly understood process. The regulation of amyloid assembly within the cell has significant relevance to several neurodegenerative disorders and further understanding of the mechanisms behind this process will provide substantial therapeutic insight. Budding yeast possess several endogenous proteins called prions that assemble into intracellular, amyloid-like fibrils. The prion [RNQ+] is toxic to yeast when the protein Rnq1 is overexpressed. Thus, the yeast prion [RNQ+] serves as a tractable, yet powerful model system to study fibril assembly and how molecular chaperones regulate this pathway to prevent the accumulation of cytotoxic species. Specifically, we find that the Type 1 Hsp40 Ydj1 interacts with the Gln/Asn rich prion domain from Rnq1 and modulates the aggregation and toxicity of this fragment. Two specific questions will be addressed: 1) What features in the yeast prion [RNQ+] regulate assembly into toxic or benign aggregates? 2) How does the Hsp40 Ydj1 maintain the Rnq1 prion domain in a benign conformation? Specific Aim 1 will investigate how full-length Rnq1 and the Gln/Asn-rich prion domain assemble into biochemically-distinct protein aggregates. We predict the efficiency of prion assembly will determine whether toxic, intermediate species accumulate when these proteins are expressed. Specific Aim 2 will address how Ydj1 interacts with the Rnq1 prion domain and buffers the accumulation of SDS-insoluble prion. Ydj1 possesses several features distinct from other Hsp40s yet shared with its human homolog Hdj-2 that may contribute to specific recognition of hydrophilic, aggregate-prone substrates. Altogether, these studies will yield additional mechanistic understanding of how molecular chaperones modulate amyloid assembly to prevent, the aberrant accumulation of toxic protein aggregates. PUBLIC HEALTH RELEVANCE: Numerous neurodegenerative disorders are caused by the accumulation of misfolded proteins within the cell. This research will examine how cells regulate the assembly of protein aggregates into toxic or benign forms.